Metallic components made of cast iron have the advantage over components produced by means of a purely mechanical process, in that they are already largely shaped during the casting. In this context, the casting material is heated to its transition into the liquid phase and is then cast in a mold. As it cools, it solidifies to give a main body with a predefined shape. In particular, more complex component shapes can thus be created. Casting may be the only method for creating some parts, or it may make production more economical. The latter generally requires relatively large production runs as the effort and the associated costs for the necessary molds may be relatively high.
Typically, for producing components by casting, use is made of suitable iron alloys which have a high proportion of carbon. This can be present as graphite or as cementite. Depending on the type of carbon present, a distinction is made between gray cast iron (graphite) or white cast iron (cementite). With respect to the mechanical properties of such cast iron, the graphite plays a role. For example, cast iron is divided into that with graphite flakes and that with spheroidal graphite.
By virtue of the advantages described in the introduction, cast iron is increasingly used in automotive construction and, in this case in particular, in the field of engine production. Following the general trend of downsizing, which generally refers to reducing weight while retaining strength properties, the material cast iron is coming back into focus. Indeed, it has been possible, for this material too, for new production methods to be developed with which it is possible to achieve higher strength values. Thus, various possibilities are now known for the heat treatment of cast iron, in order to achieve both an increase in its strength and an improvement in its elongation at break properties. In this context, a specially heat treated cast iron has been developed which is also known as austempered gray iron, or AGI for short. AGI may be extremely strong with good elongation properties, while at the same time having high fatigue strength and resistance to wear. EP 1 032 770 B1, for example, relates to an AGI in the context of brake disks. However, only the brake disk body itself is made of the AGI, wherein the wheel hub of the brake disk is made of another material. For example, the wheel hub may be formed of a normal cast iron, cast steel, or wrought steel with a tensile strength greater than 170 N/mm2. Both materials are assembled by composite casting of the wheel hub with the brake disk body, forming an integral bond point in the connection region. After turning down and hardening, this component undergoes bainitic hardening and is then polished.
However, the abovementioned advantageous properties (e.g. higher strength) are associated with extensive practical production drawbacks. In this case it is the processing, in particular the machining of components made of specially heat-treated cast iron, which proves to be very difficult on account of the increased strength and hardness. In this context, the principal drawbacks are the long processing times and the wear on the processing tools.
Taking into account the inherently positive properties of heat-treated cast iron, that is to say hardened and tempered cast iron, there may still be room for improvement, in particular in terms of its machining.
Against this background, the present disclosure includes developing a process for producing a component made of heat-treated cast iron with the aim of minimizing, overall, the finishing effort associated therewith, and thus improving the competitiveness, in terms of production costs, of components made of cast iron which is hardened and tempered in intermediate steps.